This invention relates generally to charge pumps, and in particular, to a method and apparatus for regulation of a negative output voltage charge pump.
Many applications require circuits that can boost up an input power supply DC voltage to a higher DC voltage used for specialized operations. The reason for the voltage boost up is that often only standardized power supply voltages are available for supplying power to electronic circuits. However, sometimes there are situations where a circuit needs a higher voltage than one available from the associated power supply. In addition, other circuits even require a negative voltage even though only positive voltages from a power supply are available. One example of such a circuit is an electrical erasable programmable read only memory (FEPROM), typically termed in the art as xe2x80x9cflash memory.xe2x80x9d A flash memory may require a negative voltage to perform erase operations.
One circuit typically used for generating a desired voltage from an available power supply voltage is a charge pump. Charge pumps are used often for generating a higher positive voltage from an available power supply voltage. They are not often used for generating negative voltages due to the difficulties of regulating negative voltages. It is often desirable to use active devices in the regulation circuits since they typically consume relatively less power and take up less circuit real estate. However, active devices are typically not used for handling negative voltages since forward biasing of internal p-n junctions typically results. This is because the p-substrate of these active devices is connected to ground potential. Thus, placing a negative voltage on a source of an active device will forward bias the p-substrate, which produces undesirable consequences.